(1) Field of the Invention
The present invention relates to a crankshaft bearing for an internal combustion engine, and more particularly relates to a crankshaft bearing that is used with a semicircular thrust bearing attached to each of a pair of semi-cylindrical sliding bearings that is to be combined into a cylindrical shape.
(2) Description of Related Art
A crankshaft of an internal combustion engine is supported at a journal portion thereof by a lower portion of a cylinder block of the internal combustion engine via a main bearing constituted of a pair of semi-cylindrical sliding bearings. Out of the pair of semi-cylindrical sliding bearings, one or both of the semi-cylindrical sliding bearings is or are used in combination with a semicircular thrust bearing or semicircular thrust bearings. The semicircular thrust bearing is provided by being assembled to form a flange shape along one or both of two side edges of an axial end surface (that is, the side edges in a width direction) of at least one of the semi-cylindrical sliding bearings. The assembly is performed by fitting and engaging at least two tabs, which are provided at an inner periphery of the semicircular thrust bearing spaced apart from each other, in a plurality of corresponding notches (that is, recesses) which are formed at axial side edges of the semi-cylindrical sliding bearing.
The pair of semi-cylindrical sliding bearings is formed into a cylindrical shape and is held in a split type bearing housing. And, in a free state before being incorporated into the split type bearing housing, the semi-cylindrical sliding bearing is configured in a shape in which a radius of curvature becomes gradually larger from a circumferential central region thereof toward both circumferential ends. In a state (restrained state) in which the pair of semi-cylindrical sliding bearings is incorporated into a bearing holding hole of the split type bearing housing, regions of respective butted end portion of the pair of semi-cylindrical sliding bearings are in a shape pressed and deformed toward a circle center from an initial semicircular shape (shape in the free state before being incorporated into the bearing housing) so as to conform to the shape of the bearing holding hole. In other words, each of the semi-cylindrical sliding bearings fitted to each of half bodies of the split type bearing housing before assembly is held in close contact with the bearing housing half body with its own elastic restoring force which is generated by the deformation.
More specifically, in the free state, the radius of curvature of the semi-cylindrical sliding bearing differs in the circumferential central region and both circumferential end regions. And, the radius of curvature in both the circumferential end regions is larger than in the circumferential central region. When the semicircular thrust bearing is attached to the semi-cylindrical sliding bearing by using the engagement relation of the tabs and notches (recesses), one side edge of the tab interferes with one side edge of the notch of the semi-cylindrical sliding bearing in the free state, and the semicircular thrust bearing and the semi-cylindrical sliding bearing are brought into a state in which they are mechanically coupled to each other. Accordingly, the semicircular thrust bearing and the semi-cylindrical sliding bearing can be assembled into the split type bearing housing as an integrally combined single assembly. In the assembled state, the regions of the respective butted end portions of the pair of semi-cylindrical sliding bearings are deviated toward the curvature center, and the pair of semi-cylindrical sliding bearings is deformed in accordance with the shape of the bearing holding hole. However, since the semicircular thrust bearing is located outside the split type bearing housing, it is not deformed at all. Further, the interference/coupling relation of the notches and the tabs is dissolved by deformation of the semi-cylindrical sliding bearing, and the semicircular thrust bearing becomes slightly movable in the axial direction of the crankshaft with respect to the semi-cylindrical sliding bearing. As a result, at the time of operation of the internal combustion engine, automatic positioning (alignment) is performed, in which a thrust load receiving surface of the semicircular thrust bearing comes to be parallel to a side surface of crank web which applies the axial load of the crankshaft.
The combination relations of the semi-cylindrical sliding bearings and the semicircular thrust bearings are shown in patent documents, such as JP-A-47-7011, JP-A-59-147115, JP-A-07-504017, and WO 2009/062904 A1.